A conventional quartz tuning-fork type resonator is manufactured by cutting a rock quartz, generated with an autoclave or the like, into a thin slice, forming the thin-slice quartz into a tuning-fork shape by a lithography process and quartz-specific anisotropic etching, arranging the electrodes on both sides of the thin quartz formed into the tuning-fork shape, and then mounting the thin quartz on the system.
Generally, resonators are required to be high in Q value and low in manufacturing cost. In the case of the quartz tuning-fork type inflection resonator, the specific vibration frequency must match a desired frequency (usually 32.7 kHz). The specific vibration frequency varies according to the variation of the anisotropic etching of the quartz and the variation of the electrode forming time process. A desired vibration frequency is thus obtained through frequency trimming by etching part of the resonator with a laser beam. This trimming process cost is high, which is why resonators are required to have electric characteristics that are insensitive to the manufacturing variations.
Electrical trimming that uses an external electric circuit is usually employed for such a frequency trimming method. The method is effective to suppress the process cost, and thereby it is better than laser trimming. However, when such an external electric circuit is used, the frequency change width becomes proportional to the bandwidth of the subject resonator. In the case of the quartz tuning-fork type resonator, the bandwidth is about 0.2%, which is smaller than the process variations. Therefore, the electrical trimming is insufficient to eliminate the process vibrations completely. Thus, a laser is always needed for frequency trimming.
As systems are reduced in size and LSI operation speeds are improved, size reduction and higher frequency employment are also required for resonators. When such size reduction and higher frequency employment are achieved, process variations come to affect the variations of the specific vibration frequency more.
It will thus be important for such resonators to meet the requirements of the system size reduction, higher specific vibration frequency, higher Q value, wider bandwidth, and small electric characteristic variation with respect to the process variations.